Synthesis, characterization and polymerization of using a novel soluble magnesium-titanium catalyst*

Ganugupati Satyanarayana and Swaminathan Sivaramt Division of Polymer Chemistry, National Chemical Laboratory, Pune 411008, India (Received 4 January 1993; revised 28 May 1993)

A l:2 complex of MgCI2 and (THF) was prepared by a simple Grignard decomposition reaction using Mg metal and 1,2-dichloroethane in THF as diluent. The MgC12.2THF complex formed a homogeneous solution with titanium-n-butoxide in xylene at 60°C. The soluble Mg-Ti complex in xylene polymerized ethylene under homogeneous conditions in the presence of organoaluminium compounds. The kinetic behaviour of the polymerization reaction was studied. It was observed that the presence of MgCI2 transformed the Ti centre from a dimerization to a polymerization catalyst.

(Keywords: magnesium chloride; titanium-n-butoxide; magnesium-titanium catalyst)

INTRODUCTION a Grignard decomposition reaction forms a soluble complex with titanium-n-butoxide, which in conjunction Solid catalysts based on anhydrous MgCI z and Ti halides with organoaluminium compound initiates ethylene have attracted considerable attention during the past polymerization under homogeneous conditions in xylene decade as components of high efficiency ethylene and as the solvent 11. This paper reports our results on the propylene polymerization catalysts 1. The role of MgC12 synthesis, characterization and polymerization of ethylene in these catalysts has been widely discussed in the using this novel soluble Mg-Ti catalyst. literature 2. There are, however, only a few reports of truly soluble Mg-Ti catalysts for olefin polymerization. Soga et al. prepared a soluble metal halide-2-ethylhexanol complex which, in conjunction with titanium-n-butoxide EXPERIMENTAL and diethylaluminium chloride, polymerized propylene 3. Materials This catalyst enabled the authors to study the effect of Magnesium turnings (Loba Chemicals, Bombay, India), the electronegativity of the metal in the metal halide on triisobutylaluminium (TIBAL), diethylaluminium chloride catalyst activity. Yano et al. prepared a MgCI2 2- (DEAC), triethylaluminium (TEAL), ethylhexanol complex which, in conjunction with TIC14 (TMA) and trioctylaluminium (TOAL) (all from Schering or titanium-n-butoxide and diethylaluminium chloride, AG, Bergkamen, Germany) were used as received. was used as a catalyst for high temperature polymer- 1,2-Dichloroethane (SD Fine Chemical, Bombay, India) ization of ethylene4'5. In both of these studies, whereas was distilled over Call 2 and stored over 3 A molecular the precursors were hydrocarbon soluble, the true sieves. Polymer grade ethylene was obtained from the catalyst formed by the addition of diethylaluminium Gas Cracker Complex of the Indian Petrochemical chloride was heterogeneous. Corporation Limited (Nagothane, India). It had a More recently, truly soluble Mg-Ti catalysts have been moisture content of <4ppm (Shaw model SHA-TR reported by Makino et al. 6'7 and Zucchini et al. 8 10. moisture analyzer) and oxygen content of <3ppm Reduction of TiCI4 by Grignard reagent or solubilizing (Braun oxygen analyzer). Titanium tetra-n-butoxide anhydrous MgCI 2 with trialkylphosphate was reported (TNB; Synthochem, India) was vacuum distilled twice to result in soluble Mg Ti catalysts capable of co- and was further purified by adding TIBAL (2 ml in 10 ml polymerizing ethylene with propylene6'7. Reaction of of ) to TNB (15 ml)dropwise at room temperature. anhydrous MgCI 2 with titanium-n-ethoxide in a 2:1 The colour of the solution turned black. The mixture was stoichiometry results in an isolable bimetallic complex stirred for 30min and distilled at 120°C (0.5mmHg). capable of polymerizing ethylene in a homogeneous Solvents were dried over Call 2 and distilled over Na medium in toluene s lo. wire under a positive pressure of high purity N2 or Ar. We have recently observed that a complex of anhydrous All manipulations involving air-sensitive compounds MgC12 with tetrahydrofuran (THF) prepared in situ from were performed inside a Labconco (model 50004) inert a Grignard decomposition reaction forms a soluble atmosphere glove box continuously purged with high purity N z (<5ppm) generated using a N z generator (Spantech, model NG 300-1, UK) or under a positive * NCL communicationno. 5702 pressure of high purity N 2 using standard bench-top inert t To whom correspondence should be addressed atmosphere techniques.

0032-3861/94/06/1287-04 ~) 1994 Butterworth-HeinemannLtd POLYMER Volume 35 Number 6 1994 1287 Study of a soluble Mg-Ti catalyst." G. Satyanarayana and S. Sivaram

Synthesis of MgCl 2.2THF RESULTS AND DISCUSSION A three-necked round-bottom flask equipped with a Preparation of MgCI2.2THF magnetic bar, N2 inlet, addition funnel and a reflux The THF adduct of MgC12 was prepared by a condenser was flame dried and cooled under NE single-step decomposition of Grignard reagent derived atmosphere. Iodine activated Mg turnings were placed from Mg metal and 1,2-dichloroethane in THF at 60°C: in the flask and THF was added at 40°C. 1,2-Dichloro- ethane (30ml) was added dropwise to the refluxing THF,60°C THF until all the Mg turnings dissolved. Evolution of Mg + CI-CH2-CH2-C1 ~ MgC12.2THF + C2H 4 ethylene indicating rapid decomposition of fl-chloroethyl- The solid complex precipitated out of solution. Although magnesium chloride and concomitant formation of a the facile decomposition of a Grignard reagent derived THF complex of MgCI z was observed. The solid was from Mg metal and 1,2-bromoethane is reported in the filtered and dried under vacuum for 8 h at 30°C (yield literature 13, the analogous reaction with 1,2-dichloro- 16.5g; Mg= 10.5%, C1=27.8%). ethane appears to have no precedent. Complexes of Preparation of soluble catalyst MgC12 with THF have been synthesized earlier by MgCIz.2THF (2g) was placed in a three-necked Handlir et al. 14 by the reaction of HgC12 and Mg metal round-bottom flask fitted with a condenser, N z inlet and in THF at 60°C. The complex isolated was observed to a septum. Xylene (50 ml) was added in the flask followed be insoluble in hexane or xylene even at refluxing by TNB (4 ml) using a hypodermic syringe. The slurry temperatures. was heated at 60°C in an oil bath for 8 h with stirring. Elemental analysis established the stoichiometry of the It was found that the solid slowly dissolved in the xylene complex as MgC12.2THF. The presence of THF was phase. The reaction mixture was cooled. The unreacted established by the appearance of triplets at 3.7 and MgClz.2THF was allowed to settle and the supernatant 5.7 ppm in the 1H n.m.r, spectrum in D20 as solvent and bands at 1039 and 885 cm- t in the FTl.r. spectrum. The clear liquid was transferred by a cannula into an Aldrich Sure/Seal ® bottle under N z pressure. The clear liquid powder XRD spectrum of MgC12.2THF showed strong was analysed for Ti (8.7 mg) and Mg (3.8 mg) in 1 ml of reflections at 20=29.2, 32.4 and 40.8° . In comparison, xylene solution. anhydrous MgC12 (Toho Titanium Co., Tokyo, Japan) showed all the above reflections and also a noticeable Polymerization of ethylene reflection at 20=31.5 ° which is absent in MgCI2.2THF. Polymerization was performed in a stirred glass cell at The powder XRD pattern of MgC12. 2THF is in agreement 1 atm (1 × l0 s Pa) of ethylene in xylene and hexane as with that reported in the literature but prepared by a diluents. A gas burette with a reservoir containing silicone different route ~4. The results show that the complex is oil was used to feed ethylene continuously to the cell. highly crystalline. The complex had a total pore surface The reaction cell was dried at 120°C overnight and cooled area of 10 m 2 g- 1 and a mean pore volume of 0.83 cm 3 g - 1. under N2. Solvent was introduced into the cell using a MgC12.2THF was subjected to t.g.a. (N2 atmosphere, hypodermic syringe followed by xylene soluble Mg-Ti 50-300°C, rate of 10°C min-1). The results showed that catalyst (0.2 ml) with a hypodermic syringe. The solvent the THF loss occurred in a two-stage process. The total was saturated with ethylene. Polymerization was initiated weight loss was observed to be 74% which corresponds by the addition of an organoaluminium compound. The to 2 mol of THF per of MgCI2 (Figure 1). reaction temperature was maintained by circulating water from a thermostat through the jacket of the cell Preparation of soluble Mg-Ti catalyst and the gas burette. Ethylene uptake was measured as a Under defined experimental conditions, MgCIz.2THF function of time. The reaction was terminated after 30 rain and TNB were found to be soluble in xylene at 60°C by addition of acidified methanol. The polymer was forming a homogeneous solution. The solution typically filtered and dried at 40°C under vacuum. analysed for Ti and Mg, 8.7 and 3.8 mg ml- 1, respectively. However, upon addition of hexane a solid precipitated Analysis out which, after repeated washing with dry hexane, Chlorine and magnesium estimation was performed by argentimetric and EDTA titrations, respectively. The Ti content in the catalyst was determined by the u.v. technique using a Hitachi (model 220) u.v.-visible spectro- 100 photometer lz. The n.m.r, spectrum of the support was recorded in D20 using a Briiker FT-80n.m.r. spectro- meter. The Fourier transform infra-red (FTi.r.) spectrum 75 of support was run on a Perkin-Elmer 16PC FT-IR in Nujol mull using NaCI cells (1600--400 cm-1). The E: powder X-ray diffraction (XRD) was recorded on a D3 50 Phillips PW 1730 spectrometer using Ni-filtered CuK~ o radiation. Thermogravimetric analysis (t.g.a.) was per- formed on a Perkin-Elmer TGA-7 thermal analysis work 25 station. Surface area measurements were performed by Quantachrome mercury intrusion porosimetry. The e.s.r. spectrum was run on a Briiker (model ER-200D) e.s.r. spectrometer at room temperature (9.72 GHz). Differential 40 70 100 130 160 190 220 250 280 310 340 scanning calorimetric analysis of polyethylene was per- formed on a Perkin-Elmer DSC-7 thermal analysis work Temperature (°C) station. Figure 1 Thermogravimetry of MgCIz.2THF

1288 POLYMER Volume 35 Number 6 1994 Study of a soluble Mg-Ti catalyst: G. Satyanarayana and S. Sivaram analysed for Ti and Mg, 0.2 and 1.0% per gram of isolated reaction media at a total pressure of 1 atm. The results solid. This indicates that the complex existing in solution are shown in Tables 1, 2 and 3. Even upon addition of in xylene breaks into its component constituents in the organoaluminium cocatalyst, the Mg-Ti complex hexane. Our attempts to isolate the soluble complex free showed no evidence of precipitation in xylene. Catalyst of xylene have so far been unsuccessful. activity was high with DEAC compared to trialkyl- The xylene soluble Mg-Ti complex was estimated to aluminiums in xylene (Table 1). With DEAC as cocatalyst contain 1.5 mol of TNB per mole of MgCI2.2THF. The the conversion to polymer increased with temperature. soluble catalyst showed on reduction with TIBAL a sharp The catalyst activity also increased with A1/Ti ratio. The intense signal at g=1.94 in the e.s.r, spectrum. The catalyst activity was relatively poorer with trialkyl- intensity of the signal was observed to be relatively higher aluminiums. No ethylene absorption was observed below than the signal obtained with the TNB-TIBAL catalyst an A1/Ti ratio of 100. Furthermore, polymerization system. The sharp intense signal without any fine activity decreased as the alkyl length in the organo- structure indicates that the Mg-Ti catalyst is homo- compound increased (Table 2). In hexane, the geneous in xylene. catalyst precipitated as a fluffy, white material which also polymerized ethylene, but with reduced activity (Table Polymerization of ethylene 3). However, the polymer molecular weights were higher. Ethylene polymerization was conducted using the The polyethylene obtained in all cases was observed to soluble Mg-Ti catalyst in xylene and hexane as the have a melting temperature of 135-140°C with the

Table 1 Polymerization of ethylene using soluble Mg-Ti catalyst in xylenea

A1/Ti Cocatalyst Temp. Conv. Activity [q] b Entry wt ratio (°C) (%) (gPEg I Tih-a) (dlg -a)

1 12 DEAC 70 78 397 3.2 2 50 DEAC 70 80 522 2.5 3 100 DEAC 70 80 633 1.4 4 50 DEAC 50 60 355 2.3 5 50 DEAC 30 50 231 2.5 6 100 TIBAL 70 72 35 2.9 7 200 TIBAL 70 72 35 3.1 8 200 TIBAL 30 65 30 2.8 9 200 TIBAL 50 68 39 2.7 10 200 TIBAL 70 70 40 3.1

° Polymerizations were performed at a total pressure of 1 atm for 30min ~Intrinsic viscosities were measured in o-dichlorobenzene at 135°C

Table 2 Polymerization of ethylene using soluble Mg-Ti catalyst in xylene. Effect of cocatalyst"

A1/Ti Temp. Conv. Activity [~/]b Entry wt ratio Cocatalyst (°C) (%) (g PE g- a Ti h- 1) (dl g- 1)

1 100 DEAC 70 80 633 1.4 2 100 TMAL 70 78 68 2.4 3 100 TEAL 70 75 50 2.2 4 100 TIBAL 70 72 35 2.4 5 100 TOAL 70 -

"Polymerizations were performed at a total pressure of 1 atm b Intrinsic viscosities were measured at 135°C in o-dichlorobenzene

Table 3 Polymerization of ethylene using soluble Mg-Ti catalyst in hexane a

A1/Ti Temp. Conv. Activity [q] b Entry wt ratio Cocatalyst (°C) (%) (gPEg I Tih-a) (dig -a)

1 12 DEAC 30 82 235 4.5 2 50 DEAC 30 80 275 4.3 3 100 DEAC 30 90 310 4.0 4 100 TIBAL 30 78 224 3.9 5 200 TIBAL 30 85 210 4.2 a Polymerizations were performed at a total pressure of 1 atm b Intrinsic viscosities were measured at 135°C in o-dichlorobenzene

POLYMER Volume 35 Number6 1994 1289 Study of a soluble Mg-Ti catalyst. G. Satyanarayana and S. Sivaram

24 catalyst (Mg/Ti=0.38) promoted ethylene polymeriza- tion to a high molecular weight linear polyethylene. The 22 results are best understood in terms of bimetallic species formed by the cleavage of the distorted orthorhombic 20 structure of MgCI2.2THF 18 by the tetrameric TNB. The chlorine ligands of MgC12 thus contribute to the stability 18 of the Ti-C bond resulting in the polymerization activity. Thus, in these catalyst systems, MgCI 2 exerts a subtle yet 16 significant influence on the nature of the Ti active centre in transforming it from a dimerization to a polymerization 14 catalyst. lul 12 O_ ACKNOWLEDGEMENTS I0 GS thanks the Council of Scientific and Industrial Research, India for the award of a senior research 8 fellowship. Financial assistance from the Department of • ~.,eB 6 -.-...a.. A Science and Technology, India, under the Integrated Long Term Program, is gratefully acknowledged. We

4 thank Synthochem, Indore for the generous gift of TNB.

2 REFERENCES ol 1 Barbe, P. C., Cecchin, G. and Noristi, L. Adv. Polym. Sci. 1986, o 5 10 15 20 25 30 81, 1 2 Chien, J. C. W. Catal. Rev. Sci. Eng. 1984, 26, 613 Time (rain} 3 Soga, K., Shiono, T., Wu, Y. Y., Ishii, K., Nogami, A. and Doi, Y. Figure 2 Plot of the rate of polymerization versus time for the Makromol. Chem. Rapid Commun. 1985, 6, 537 Mg-Ti/DEAC catalystsystem. [Ti] = 3.6 × 10-5 mol. A1/Ti:(A) 12; (B) 4 Yano, T., Ikai, S., Shimizu, M. and Washio, K. J. Polym. Sci., 50; (C) 100 Polym. Chem. Edn 1985, 23, 1455 5 Yano, T., Ikai, S. and Washio, K. J. Polym. Sci., Polym. Chem. Edn 1985, 23, 3069 6 Makino, K., Tsuda, K. and Takaki, M. Polym. Bull. 1991,26, 371 percentage of X-ray crystallinity varying between 60% 7 Makino, K., Tsuda, K. and Takaki, M. Polym. Bull. 1991, 27, 41 and 70%. 8 Zucchini, U. and Dall'Occo, T. in 'Polymer Science: Contem- A kinetic investigation of ethylene polymerization on porary Themes' (Ed. S. Sivaram), Vol. 1, Tata-McGraw-Hill, xylene soluble Mg-Ti catalyst was conducted. A plot of New Delhi, 1991, p.221 9 Malpezzi, M., Zucchini, U. and Dall'Occo, T. Inorg. Chem. Acta versus (Figure 2) the rate of polymerization (Rp) time 1990, 180, 245 showed a steady-state kinetic curve at low A1/Ti ratio or 10 Abis, L., Bacchilega, G., Spera, S., Zucchini, U. and Dall'Occo, T. temperature up to 50°C in xylene medium. At tempera- Makromol. Chem. 1991, 192, 981 tures above 50°C and with AI/Ti > 50, the kinetic plots 11 Satyanarayana, G. and Sivaram, S. Polym. Mater. Sci. Eng. progressively changed into a decay-type curve indicating 1992, 67, 57 12 Vogel, A. I. 'A Textbook of Quantitative Inorganic Analysis', a competing deactivation process. The Arrhenius plot of 3rd Edn, 1961 log R o versus time was linear with an overall activation 13 Mauret, P. and Alphonse, P. J. Organometal. Chem. 1984, 276, energy of 3-4 kcal mol- 1 (13-17 kJ mol - 1). This value is 249 similar to that observed for homogeneous catalysts in 14 Handlir, K., Holecek, J. and Benes, L. Collect. Czech. Chem. Commun. 1985, 50, 2422 the Group IV metallocene-aluminoxane system 15. 15 Chien, J. C. W. and Wang, B. J. Polym. Sci., Polym. Chem. Edn TNB in conjunction with organoaluminium com- 1989, 27, 1539 pounds is known to promote only selective dimerization 16 Muthukumaru Pillai, S., Ravidranathan, M. and Sivaram, S. of ethylene to butene-116. We reported earlier that a Chem. Rev. 1986, 86, 353 soluble MgCI2.TNB complex (Mg/Ti=0.23) can be 17 Sivaram, S., Shashikant and Gupta, V. K. Am. Chem. Soc. Div. Petrol. Chem. Prepr. 1989, 34, 595 obtained by a thermochemical reaction of TNB and 18 Sarma, R., Ramirez, F., MeKeever, B., Chaw, Y. F., Marecek, anhydrous MgC12 which promoted selective dimerization J. F., Nierman, D. and McCaffrey, T. M. J. Am. Chem. Soc. of ethylene to butene-1 z7. In contrast, the soluble Mg-Ti 1977, 99, 5289

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